01 - Preheat the oven to 400°F (200°C) and line a baking tray with parchment paper.
02 - Heat the sunflower oil in a skillet over medium-high heat. Add the diced steak and sear for 2–3 minutes until evenly browned on all sides.
03 - Add the chopped onion and cook for another 2 minutes until softened, then stir in the minced garlic for 1 minute until fragrant.
04 - Stir in Worcestershire sauce, English mustard (if using), sea salt, and black pepper. Remove from heat and allow the mixture to cool slightly.
05 - Unroll the puff pastry sheet onto a lightly floured surface and cut into four equal rectangles.
06 - Spoon the steak mixture evenly along one long side of each pastry rectangle. Top each with grated cheddar cheese. Fold the pastry over the filling, pinching the edges firmly to seal, and place seam-side down on the prepared baking tray.
07 - Brush each roll generously with beaten egg to achieve a rich golden finish during baking.
08 - Bake for 20–25 minutes until the pastry is puffed and golden brown. Allow to cool slightly before serving.